is liable to be blown away from her moorings; an accident which
has been productive of the most disastrous consequences to life and
property.

The details already given will convey some notion of the difficulty
and danger of planting a lighthouse on the solid rock in a stormy sea;
we may naturally suppose that this difficulty and danger must be
enormously increased in erecting a permanent residence on the shifting
sands. Such, however, is by no means the case; one of the recent
triumphs of engineering has proved that it is not always folly to
build a house upon the sand.

This remarkable result has been accomplished chiefly by means of
Mitchell's screw-mooring, an instrument which consists essentially of
an enormous cast-iron screw of about one turn and a half, having a
hollow cylindrical centre; a wrought-iron spindle passes through the
cylindrical socket; it is somewhat tapering in form, and when driven
up tight is fixed thereto by a forelock passing through both; it is
formed with a square head to receive the key for screwing it into the
ground. It is also furnished with a collar of wrought iron fitted so
as to turn freely on the upper part of the shaft of the spindle below
the collar.

The attention of the Trinity House having been called to this
instrument, it was considered applicable to the establishment of
lighthouses on sands; and accordingly a series of experiments was
undertaken at the cost of that honourable body. The spot selected for
the purpose was on the verge of the Maplin Sand lying at the mouth of
the Thames, about twenty miles below the Nore, forming the north side
of the Swin or King's Channel, which, on account of its depth, is much
frequented by large ships, as also by colliers and other vessels from
the north sea. The sand is shifting, and is dry at low water
spring-tides, and hitherto a floating light has been maintained upon
it. On this spot it was proposed to erect a fixed lighthouse of timber
framing, with a lantern and residence for the attendants.

In the month of August 1838, operations were commenced by inserting
nine of Mitchell's patent mooring-screws, each four feet and a half in
diameter, and furnished with shafts of wrought iron about twenty-five
feet in length and five inches thick. One of these screws served as a
centre to the remainder, which occupied the angles of an octagon
forty-two feet in diameter. The screws were turned into the sands to
the depth of twenty-one feet an